Methods of fabricating oxide/metal composites and components produced thereby

ABSTRACT

Methods for producing oxide/metal composite components for use in high temperature systems, and components produced thereby. The methods use a fluid reactant and a porous preform that contains a solid oxide reactant. The fluid reactant contains yttrium as a displacing metal and the solid oxide reactant of the preform contains niobium oxide, of which niobium cations are displaceable species. The preform is infiltrated with the fluid reactant to react its yttrium with the niobium oxide of the solid oxide reactant and produce an yttria/niobium composite component, during which yttrium at least partially replaces the niobium cations of the solid oxide reactant to produce yttria and niobium metal, which together define a reaction product. The pore volume of the preform is at least partially filled by the reaction product, whose volume is greater than the volume lost by the solid oxide reactant as a result of reacting yttrium and niobium oxide.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/802,466 filed Feb. 7, 2019, the contents of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

The present invention generally relates to high temperature compositesand components comprising such composites. The invention particularlyrelates to methods of fabricating net-shape/size composites containing ahigh-melting oxide and a thermally-conductive refractory metal,including but not limited to components formed therefrom that arecapable of use in hypersonic applications and other high temperaturesystems.

New hypersonic components and vehicles require advanced, high-meltingmaterials that are thermally, chemically, and mechanically robustmaterials. Also required are cost-effective methods for manufacturingsuch materials and components in complex (preferably near net) shapes.One class of such robust materials is composites of ceramics withrefractory metals.

BRIEF DESCRIPTION OF THE INVENTION

The present invention generally provides mechanically-robust,thermally-robust, and chemically-robust oxide/metal composite materialsfor high temperature applications, components comprising suchoxide/metal composite materials, methods of manufacturing suchcomponents, and systems comprising such components.

According to one aspect of the invention, a method of producing anoxide/metal composite component for use in a high temperature systeminvolves providing a fluid reactant and a porous preform that has a porevolume and contains a solid oxide reactant that defines a solid volumeof the porous preform. The fluid reactant comprises at least yttrium asa displacing metal and the solid oxide reactant of the preform comprisesat least niobium oxide in which niobium cations in the niobium oxide aredisplaceable species. The yttrium of the fluid reactant is capable ofdisplacing the niobium cations in the solid oxide reactant to produce atleast yttria (yttria is used to refer herein to yttrium oxide) as asolid oxide reaction product and niobium metal as a solid metal reactionproduct. The porous preform is then infiltrated with the fluid reactantto react the yttrium of the fluid reactant with the niobium oxide of thesolid oxide reactant to produce the oxide/metal composite component,during which the yttrium of the fluid reactant at least partiallyreplaces the niobium cations of the solid oxide reactant to produce theyttria and the niobium metal that together define a reaction productvolume. The pore volume is at least partially filled by the reactionproduct volume, the reaction product volume is greater than the solidvolume lost by the solid oxide reactant as a result of the reaction ofthe yttrium and the niobium oxide, and the oxide/metal compositecomponent comprises an yttria/niobium composite containing at leastyttria and niobium metal.

Another aspect of the invention is the oxide/metal composite componentproduced by methods as described above.

Technical effects of methods as described above preferably include theability to produce components of ceramic/refractory metal compositesthat are thermally, chemically, and mechanically robust and can beproduced by a cost-effective method to have complex and preferably nearnet shapes.

Other aspects and advantages of this invention will be appreciated fromthe following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 1C schematically illustrate a displacive compensationof porosity (DCP) process by which an yttrium-bearing liquid, (Cu—Y),infiltrates a porous niobium oxide (Nb₂O₅) preform (FIG. 1A) andundergoes a pore-filling liquid/solid displacement reaction (FIG. 1B) toyield a dense net-size Y₂O₃/Nb cermet (FIG. 1C).

DETAILED DESCRIPTION OF THE INVENTION

The present invention generally provides oxide/metal composites andoxide/metal composite components, and most particularly oxide/refractorymetal composite components suitable for high temperature applications,methods of manufacturing such components, and systems comprising suchcomponents. Such high-temperature systems include, but are not limitedto, hypersonic applications that include, but are not limited to,aircraft, spacecraft, missiles, and energy conversion devices. Suchoxide/metal composite components suitable for use in high temperaturesystems include, but are not limited to, components that form theleading edges of hypersonic aircraft, spacecraft, missiles, and energyconversion devices, which may be subjected to temperatures exceeding500° C. and up to at least 2000° C. According to a nonlimiting aspect ofthe invention, the components may be manufactured to be near-net shapeand near-net size, and exhibit desirable high-temperature propertiessuch as high melting temperatures, stiffness, creep resistance, fractureresistance, erosion resistance, plastic deformation resistance, thermalcycling resistance, thermal shock resistance, corrosion resistance,thermal conductivity, electrical conductivity, and/or oxidationresistance at temperatures of at least 500° C. and up to at least 2000°C.

In order to manufacture oxide/metal composite components suitable foruse in high temperature applications, and in particular having hightemperature properties such as described above, the components arepreferably formed to near-net shape and near-net dimensions by acost-effective, shape-preserving, pressureless reactive infiltrationprocess referred to herein as a displacive compensation of porosity(DCP) process. Such processes are described in detail in U.S. Pat. Nos.6,407,022; 6,598,656; and U.S. Pat. No. 6,833,337 to Sandhage et al.,the contents of which are incorporated herein by reference in theirentirety.

Briefly, DCP processes include synthesis or other acquisition of aporous preform with an appropriate composition and pore fraction, andpreferably having the overall shape of the intended component. The porefraction of the preform is tailored so that a reaction-induced increasein solid volume can compensate partially or completely for suchporosity. From the following discussion it will be appreciated that theporous preform need only be sufficiently dimensionally stable to resistthe capillary action of an infiltrated fluid reactant. The porouspreform is infiltrated with the fluid reactant, which is caused to reactpartially or completely with the solid preform to produce a dense,shaped body containing the desired ceramic and refractory metal phases.A phase is defined herein as a homogeneous volume of matter. Thisreaction is a displacement reaction of the following general typebetween a metal species, {M}, of the fluid reactant and a ceramiccompound, NAOB(s), of the solid shaped porous preform, serving as asolid oxide reactant.

C{M}+N_(A)O_(B)(s)=M_(C)O_(B)(s)+AN(s)

M_(C)O_(B)(s) is a solid oxide reaction product, N(s) is a solid metalreaction product, and A, B and C are molar coefficients. Reactions arechosen such that the solid reaction products (i.e., AN(s) and/orM_(C)O_(B)(s)) possess a volume that is larger than the solid oxidereactant, N_(A)O_(B)(s), consumed by the reaction. Such an increase insolid volume upon reaction is used to completely fill the original porespaces within the initial porous N_(A)O_(B)(s) preform; that is, thedisplacement reaction is used to compensate for (i.e., fill) the priorpore volume (displacive compensation of porosity).

According to a preferred aspect of the invention, oxide/refractory metalcomposite components suitable for hypersonic applications comprise orconsist of an Y₂O₃/Nb composite. Y₂O₃ (yttria) and Nb (niobium metal)are each high melting materials (2404° C. and 2469° C., respectively)and are chemically compatible with each other (that is, a displacementreaction between Nb and Y₂O₃ is not thermodynamically favored). Unlikemany ceramic/metal composites, Y₂O₃ and Nb possess very similarcoefficients of thermal expansion (CTE). As shown in the Table 1 below,the values of linear expansion (ΔL/L_(o)) of polycrystalline Y₂O₃ and Nbagree to within 10% over a wide temperature range, starting at 250° C.(or lower) and up to and including at least 2000° C.

TABLE 1 Percentage of linear expansion, 100 · ΔL/L₀ (relative to roomtemperature) Material 250° C. 500° C. 750° C. 1000° C. 1250° C. 1500° C.1750° C. 2000° C. Y₂O₃ 0.16% 0.34% 0.54% 0.76% 1.00% 1.26% 1.54% 1.84%Nb 0.17% 0.37% 0.58% 0.80% 1.03% 1.27% 1.49% 1.76%

The ductility of the Nb phase over a wide range of temperatures isbelieved to endow the oxide/metal composite components with enhancedtoughness (relative to monolithic Y₂O₃). Such ductility, coupled withthe similar CTE values of Nb and Y₂O₃, also provide for enhanced thermalshock resistance. An interconnected Y₂O₃ phase in such compositesshould, in turn, enhance the high-temperature stiffness of thecomponents (relative to monolithic Nb).

The composite components may be fabricated in complex and preferablynear net shapes by the DCP process on the basis of the followingdisplacement reaction between a yttrium-bearing liquid as the fluidreactant and solid Nb₂O₅ as the solid oxide reactant of the preform,whereby yttrium of the fluid reactant at least partially replaces theniobium cations in the niobium oxide of the solid oxide reactant toproduce yttria and niobium metal.

10{Y}+3Nb₂O₅(s)=>5Y₂O₃(s)+6Nb(s)  (1)

The fluid reactant, {Y}, may comprise or consist of yttrium dissolvedwithin a Cu—Y liquid, such as a CuiYi liquid (CuiYi melts congruently at947° C., which is appreciably lower than the 1522° C. melting point ofpure Y). In addition to acting as an effective solvent for yttrium,copper does not form any compounds with niobium, and niobium exhibitsonly slight solubility in liquid copper (e.g., <1 wt % at 1150° C.).Yttrium and niobium also do not react to form any intermetalliccompounds, and exhibit negligible mutual solid solubility (i.e., niobiummetal formed by reaction (1) will not undergo further reaction withyttrium to form any Nb—Y compounds). Reaction (1) is highlythermodynamically favored at modest temperatures (e.g., ΔG° rxn(1)[1127°C.] is −3,639 kJ per mole of reaction). Furthermore, the total volume ofthe solid products of this reaction (5 moles of Y₂O₃ and 6 moles ofNb=290 cm³) is significantly larger than the volume of the solidreactant (3 moles of Nb₂O₅=176 cm³).

V _(Solid Products)[6Nb+5Y₂O₃]>V _(Solid Reactant)[3Nb₂O₅]

Consequently, a porous, near net shape preform of Nb₂O₅ can be convertedvia the liquid/solid displacement reaction (1) into a dense Y₂O₃/Nbcomposite; that is, the displacement reaction can be used to entirelyfill the pores in the preform.

The phase content of the final Y₂O₃/Nb composite can be adjusted over awide range via control of the Nb₂O₅ preform porosity and by controlledadditions of additional Nb metal to the Nb₂O₅ in the preform for thepurpose of adjusting (increasing) the total niobium (both oxide andmetal) content of the preform.

While it expected that dense, thermal shock resistant, net-shape Y₂O₃/Nbcomposites can be fabricated by the reactive infiltration-based DCPprocess, the Nb in such composites may not be adequately resistant tooxidation, particularly at high temperatures and high oxygen partialpressures. To inhibit Nb oxidation, the Y₂O₃/Nb composite may be coatedwith a dense layer that inhibits oxygen diffusion. A particular butnonlimiting example is a dense layer (coating) of Y₂O₃ that may bedeposited by various deposition processes. As an example, an yttrialayer can be generated by processes that use various forms of physicalvapor deposition, chemical vapor deposition, or air plasma spraying, orby one or more of: a sol-gel dip coating and firing process, a powderslurry dip coating and firing process, a slip casting process, a laserdeposition process, a plasma spraying process, a flame spraying process,an electrophoretic deposition process, and a hot isostatic pressingprocess. A final high-temperature firing process may be used to promotediffusion bonding of the Y₂O₃ layer to the surface of the Y₂O₃/Nbcomposite. Oxygen diffusion through dense Y₂O₃ has been found to be veryslow. The following Arrhenius relation has been reported for oxygenlattice diffusion through Y₂O₃ over a temperature range of 1100-1500° C.

D _(O)=7.3×10⁻⁶ exp[−191 kJ/RT]cm²/sec  (2)

Extrapolation of this equation to 2200° C. yields a value ofD_(o)=6.7×10⁻¹° cm²/sec. For a time of 30 minutes at 2200° C., thisvalue of D₀ yields an effective diffusion distance, (Dt)^(1/2), of only1.1×10⁻³ cm (11 μm). Hence, a 100 μm thick (0.1 mm) or thicker Y₂O₃coating on an Y₂O₃/Nb composite should endow the composite with adesirable level of oxidation resistance for low-altitude hypersonicflight.

While high-melting, Y₂O₃-coated, Y₂O₃/Nb composites are believed topossess a desirable resistance to oxidation and thermal shock attemperatures in excess of 2200° C., other potential oxide-coated,oxide/refractory metal composites that can be fabricated by thenet-shape DCP process are foreseeable, including other combinations ofhigh-melting oxides and refractory metals (e.g., W, Mo, Ta, Nb, Hf,etc.).

The DCP process is particularly well suited for producing the Y₂O₃/Nbcomposites, as it provides a cost-effective method for fabricatingnet-shape and net-size oxide/metal composites, i.e., without thesintering shrinkage encountered in conventional ceramics processing andwithout the need for appreciable costly machining, or chemical etchingof metallic alloys. The resulting composite components may have highmelting temperatures, may be mechanically robust, thermally robust, andchemically robust, and may be thermally and/or electrically conductive.As such, the application of such oxide/metal composite components formedby the DCP process to high-temperature systems provides significantadvantages over conventional high-temperature metallic alloys or ceramiccomposites made by conventional methods.

While the invention has been described in terms of specific orparticular embodiments, it should be apparent that alternatives could beadopted by one skilled in the art. For example, the components couldhave different compositions than those described herein, processparameters such as temperatures and durations could be modified, andappropriate materials could be substituted for those noted. Accordingly,it should be understood that the invention is not necessarily limited toany embodiment described herein. It should also be understood that thephraseology and terminology employed above are for the purpose ofdescribing the disclosed embodiments, and do not necessarily serve aslimitations to the scope of the invention. Therefore, the scope of theinvention is to be limited only by the following claims.

1. A method for producing an oxide/metal composite component for use ina high temperature system, the method comprising: providing a fluidreactant and a porous preform that has a pore volume and contains asolid oxide reactant that defines a solid volume of the porous preform,the fluid reactant comprising at least yttrium as a displacing metal andthe solid oxide reactant of the preform comprising at least niobiumoxide in which niobium cations in the niobium oxide are displaceablespecies, the yttrium of the fluid reactant being capable of displacingthe niobium cations in the solid oxide reactant to produce at leastyttria as a solid oxide reaction product and niobium metal as a solidmetal reaction product; and infiltrating the porous preform with thefluid reactant to react the yttrium of the fluid reactant with theniobium oxide of the solid oxide reactant to produce the oxide/metalcomposite component, during which the yttrium of the fluid reactant atleast partially replaces the niobium cations of the solid oxide reactantto produce the yttria and the niobium metal that together define areaction product volume, the pore volume is at least partially filled bythe reaction product volume, and the reaction product volume is greaterthan the solid volume lost by the solid oxide reactant as a result ofthe reaction of the yttrium and the niobium oxide, wherein theoxide/metal composite component comprises an yttria/niobium compositecontaining at least yttria and niobium metal.
 2. The method of claim 1,wherein the fluid reactant further comprises copper.
 3. The method ofclaim 2, wherein the fluid reactant is a Cu—Y liquid.
 4. The method ofclaim 1, further comprising exposing the oxide/metal composite componentto temperatures greater than 500° C. in the high temperature system,wherein the yttria and the niobium metal exhibit linear thermalexpansion values within 10% of one another over a temperature range of250° C. to at least 2000° C.
 5. The method of claim 4, wherein the hightemperature system is a hypersonic application.
 6. The method of claim5, wherein the hypersonic application is chosen from the groupconsisting of aircraft, spacecraft, missiles, and energy conversiondevices.
 7. The method of claim 1, wherein the oxide/metal compositecomponent is a component at a leading edge of a hypersonic aircraft,spacecraft, missile, or energy conversion device.
 8. The method of claim1, further comprising adjusting amounts of the yttria and the niobiummetal in the oxide/metal composite component by adding additionalniobium metal to the porous preform prior to the infiltrating step. 9.The method of claim 1, further comprising forming an yttria coating onthe oxide/metal composite component.
 10. The method of claim 9, whereinthe yttria coating is generated by one or more of physical vapordeposition, chemical vapor deposition, and air plasma spraying.
 11. Themethod of claim 9, wherein the yttria coating is generated by one ormore of: a sol-gel dip coating and firing process, a powder slurry dipcoating and firing process, a slip casting process, a laser depositionprocess, a plasma spraying process, a flame spraying process, anelectrophoretic deposition process, and a hot isostatic pressingprocess.
 12. The oxide/metal composite component produced by the methodof claim
 1. 13. A method for producing an oxide/metal compositecomponent for use in a high temperature system, the method comprising:providing a fluid reactant and a porous preform that has a pore volumeand contains a solid oxide reactant that defines a solid volume of theporous preform, the fluid reactant comprising a Cu—Y liquid thatcontains yttrium as a displacing metal and the solid oxide reactant ofthe preform consisting of niobium oxide in which niobium cations in theniobium oxide are displaceable species, the yttrium of the fluidreactant being capable of displacing the niobium cations in the solidoxide reactant to produce yttria as a solid oxide reaction product andniobium metal as a solid metal reaction product; infiltrating the porouspreform with the fluid reactant to react the yttrium of the fluidreactant with the niobium oxide of the solid oxide reactant to producethe oxide/metal composite component, during which the yttrium of thefluid reactant replaces the niobium cations of the solid oxide reactantto produce the yttria and the niobium metal that together define areaction product volume, the pore volume is filled by the reactionproduct volume, and the reaction product volume is greater than thesolid volume lost by the solid oxide reactant as a result of thereaction of the yttrium and the niobium oxide, wherein the oxide/metalcomposite component comprises an yttria/niobium composite containingyttria and niobium metal; and forming an yttria coating on theoxide/metal composite component.
 14. The method of claim 13, furthercomprising exposing the oxide/metal composite component to temperaturesgreater than 500° C. in the high temperature system, wherein the yttriaand the niobium metal exhibit linear thermal expansion values within 10%of one another over a temperature range of 250° C. to at least 2000° C.15. The method of claim 14, wherein the high temperature system is ahypersonic application.
 16. The method of claim 15, wherein thehypersonic application is chosen from the group consisting of aircraft,spacecraft, missiles, and energy conversion devices.
 17. The method ofclaim 13, wherein the oxide/metal composite component is a component ata leading edge of a hypersonic aircraft, spacecraft, missile, or energyconversion device.
 18. The method of claim 13, further comprisingadjusting amounts of the yttria and the niobium metal in the oxide/metalcomposite component by adding additional niobium metal to the porouspreform prior to the infiltrating step.
 19. The oxide/metal compositecomponent produced by the method of claim
 13. 20. A method for producingan oxide/metal composite component for use in a high temperature system,the method comprising: providing a fluid reactant and a porous preformthat has a pore volume and contains a solid oxide reactant that definesa solid volume of the porous preform, the fluid reactant comprising atleast one metal as a displacing metal and the solid oxide reactant ofthe preform comprising at least one oxide in which cations of the oxideare displaceable cation species, the displacing metal of the fluidreactant being capable of displacing the cations in the solid oxidereactant to produce at least a solid oxide reaction product and a solidmetal reaction product; and infiltrating the porous preform with thefluid reactant to react the displacing metal of the fluid reactant withthe displaceable cation species of the solid oxide reactant to producethe oxide/metal composite component, during which the displacing metalof the fluid reactant at least partially replaces the displaceablecation species of the solid oxide reactant to produce the solid oxidereaction product and the solid metal reaction product that togetherdefine a reaction product volume, the pore volume is at least partiallyfilled by the reaction product volume, and the reaction product volumeis greater than the solid volume lost by the solid oxide reactant as aresult of the reaction of the displacing metal and the solid oxidereactant, wherein the oxide/metal composite component comprises anoxide/metal composite.
 21. The method of claim 20, wherein the solidmetal reaction product of the oxide/metal composite comprises one ormore of tungsten, molybdenum, tantalum, niobium, and hafnium, and thesolid oxide reaction product of the oxide/metal composite possesseslinear thermal expansion values within 10% of linear thermal expansionvalues of the solid metal reaction product over a temperature range of250° C. to at least 2000° C.
 22. The oxide/metal composite componentproduced by the method of claim 21.